There is an increasing interest in being able to noninvasively inspect the contents of such large objects as automobiles, trucks, rail cars and the international shipping containers used at seaports and airports. The objectives of such inspections are varied and include the detection of contraband at ports of entry; the detection of explosives at entrances to buildings or within baggage and containers; and, for commercial reasons, such as verifying the accuracy of customs declarations and shipping manifests.
This invention, in particular, addresses the growing problem of stolen cars being shipped to other countries for resale. The National Insurance Crime Bureau estimates that of the 1.5 million vehicles stolen annually in the U.S.A., 200,000 are shipped overseas. This costs insurance companies and consumers $1 billion to $4 billion annually. A principal method for exporting these stolen vehicles is to conceal them within the large, international, ocean-going shipping containers which are up to 44-ft long. Since one container can contain four automobiles and some ships can hold approximately 4,000 containers, the potential for loss is large and the problem of detection is considerable. Containers are loaded and closed at their departure point. The physical inspection of a high percentage of containers by U.S. Customs personnel is not a practical solution. It has been estimated that 15 person hours are required to unload and inspect a container. In addition to the direct cost of physical inspection, the delivery of the container is correspondingly delayed and such inspections break the shipper's trust and invalidates the carrier's insurance, opening up the possibility of claims for loss and damage.
An example is provided by the Port of Miami. Nearly 10,000 cargo vessels dock at Miami every year, unloading 35 million tons of freight. Tonnage at the port is growing at an annual rate of 10 percent. Currently, U.S. Customs can physically inspect less than 3 percent of the 200,000 ocean-going containers that enter Miami every year. Moreover, the Customs inspectors emphasize incoming cargo and a somewhat smaller fraction of exiting cargo is inspected. The Miami airport handles most of the U.S. air traffic for Central and South America with very large numbers of air cargo containers. While these containers are too small to conceal cars, other contraband is sometimes present, particularly upon import to the U.S.
Noninvasive inspections using X-ray beams to image the contents of containers as well as vehicles and rail cars are considered to be one of the most practical approaches to contraband detection and manifest verification. Many nations are implementing some form of X-ray imaging. In the U.S., a prototype system by Analytical Systems Engineering Corp. for inspecting containers was evaluated at the Port of Tacoma. U.S. Customs is employing X-ray inspection systems manufactured by American Science and Engineering at the U.S.-Mexican border to search for contraband in cars and trucks. In Europe, X-ray systems by Europscan of France have been installed at either end of the Eurotunnel (Channel Tunnel) to detect explosives in vehicles. Two X-ray systems (one Heimann; one British Aerospace) have been installed at the Hong Kong-China border for verifying the contents of trucks and truck-borne shipping containers. Large X-ray systems were also installed at the Port of LaHavre, France (Europscan) and the Port of Hamburg, Germany (Heimann).
There have been several patents issued that cover variations of the fixed-site inspection approach. For example, U.S. Pat. No. 4,366,382 to Kotowski discloses a fixed-site baggage inspection system that uses a conveyor belt to pass baggage between an X-ray beam and a line array of detectors.
Likewise, U.S. Pat. No. 4,430,568 to Yoshida presents an X-ray system for the inspection of packages, including large shipping containers. Here again, the system is installed in a fixed site and employs a conveyor to move the package or container between the X-ray source and detector array.
U.S. Pat. No. 4,599,740 to Cable discloses another variation of the fixed-site inspection approach, particularly addressing the inspection of large items such as international shipping containers. Although the system of this patent again is in a fixed site and uses a conveyor to move the container between the X-ray source and the detectors, the invention relates to the use of a "folded" sensor screen or device that requires less height than previous straight detector arrays.
U.S. Pat. No. 5,237,598 to Albert discloses a mobile system for large objects such as aircraft, boat hulls or lengthy pipelines. This invention instead of using a small X-ray spot and a large detector array for imaging large objects, employs a large area source and a single X-ray detector, or plurality of individual detectors spaced over the objects, which has a small X-ray sensitive area. Using this "reverse geometry" approach, an image is obtained of an area of the object approximately equal to the area of the source. By moving the source to the location of another detector, or by moving the object relative to the source, other areas of the object can be inspected in sequence. The principal advantage cited for this approach is that precise alignment is not required between the source and the detector, therefore, the source and detector do not have to be secured with respect to one another.
Except for the Albert patent, these systems have an objective related to that of the present invention--the noninvasive X-ray inspection of large objects, such as vehicles and international shipping containers. However, they all are different from the present invention in several fundamental ways. All of the systems installed to date are of the "car wash" type, i.e., they are permanently installed in large shielded structures, thus requiring that the object to be inspected (container, truck, car, etc.) be brought to the facility. Once at the facility, some form of conveyance is employed to transport the container or vehicle through the stationary X-ray source and detectors. Then, the conveyance must be returned to the starting point to pick up another container or car. This is a time consuming operation. The "car wash" inspection facility has a number of problems that will limit its use, especially at ports which are typically spread out over many areas, congested, and with a large number of separate terminals. As an example, the prototype X-ray inspection facility evaluated at the Port of Tacoma had to be located a few miles from the docks, was in a 6-acre site and employed an X-ray examination building that was 242 feet long. Furthermore, the inspection system had a reported throughput capability of only four to six vehicles or containers per hour. Thus, it is obvious that cost and logistics issues prevent the use of fixed-site X-ray inspection facilities at most, if not all, ports. The patent to Albert, on the other hand, deals with a mobile system in which the large area X-ray source required is limited to low energies. Thus, this system is primarily useful for thin walls of aircraft or ship hulls, not for highly attenuating vehicles or cargo containers.